How are barrels rifled? – Part 3Hammer-forged barrels

Hammer-forging, also called rotary forging today, is the high-rate production way to make a rifle barrel. The process takes three to four minutes, start to finish.

The hammer-forging process itself is actually close to two centuries old. It was used by gunsmiths in Appalachia, who hand-hammered steel barrel blanks around mandrels to make barrels for the famous Tennessee Poor Boy rifles of the 19th century. They used a special “gun anvil” that had a special hammer fitted to it. The barrel blank was placed between the hammer and anvil. The special hammer was struck by a conventional hammer to form the steel.

Cold formedA modern hammer-forged barrel is formed by beating on a steel tube with multiple hammers until the steel forms itself around a tungsten carbide mandrel. Believe it or not, the correct alloy of cold steel will flow like toothpaste when the circumstances are right. The mandrel is engraved with a reverse of the rifling pattern. When the steel conforms to it, it takes on the exact pattern the maker desires. The hammers strike the steel tube about half-million times during the forming process, and they leave a pattern on the outside and inside of the barrel. Some companies remove this pattern, while others, like Mannlicher and Ruger, proudly show it off.

Ruger proudly displays the marks of hammer forging, seen in this enlargement of their 10/22 Target bull barrel as spiral flats running the length of the barrel. The marks running across the flats (top to bottom in this picture) are tiny grooves in the steel that opened up during the forming process. You can see these rough marks only under magnification and the right lighting.

The blank steel tube is fatter and about 30 percent shorter than the finished barrel will be. When the barrel is finished, a lot fewer operations need to be performed than with barrels rifled by other methods. The bore comes out glass-smooth and very hard from the hammering process. That hardness resists erosion from the heat of the combustion gasses of a firearm cartridge, thus prolonging the life of the barrel.

On the negative side, hammer-forging introduces stress points that must be relieved or the barrel will warp when it heats up. So, target shooters don’t pick hammer-forged barrels. It isn’t as critical for rimfires as it is for centerfire cartridges, so Ruger gets away with hammer-forging its 10/22 Target barrel. The only way a centerire rifle can get away with one is to have a lot of stress relief after the barrel is made.

Of course, airguns produce no heat to speak of when they fire; so, the barrel stress points are not critical, and target air rifles and air pistols are a possibility. We know that IZH makes hammer-forged barrels, and there are probably other companies who do as well.

Why doesn’t everyone do it?A new hammer-forging machine costs $750,000 or more, making it a large capital investment. When a button-rifling setup costs $50,000, or so, it’s hard to justify the more expensive process unless the demand for barrels is very high, as each barrel has to carry an amortized share of the machine’s cost. Only companies making thousands of barrels per month can afford to do it this way.

There is no particular advantage to a hammer-forged barrel on an airgun, nor is there any disadvantage. If a maker can afford a machine, it can pump out a lot of barrels, but there has to be a market for them.

The term magnum has been adapted to advertising and has lost all meaning when applied to products.

In the 1970s, a magnum air rifle shot at least 800 f.p.s. Today, with rifles like the Condor capable of over 1,400 f.p.s. the term magnum has no meaning, other than an advertising term that attempts to convey the sense of great power.

I have a theory about that. Whenever I see diablo instead of diabolo I imagine that whoever is in charge of product packaging just doesn’t know better. But that’s not always the case.

Some British pellet makers think it’s funny to name their pellets diablo, making them a diablo diabolo. I guess that seems funny. It makes my job a lot harder, just like when the Benjamin Air Rifle Co. put “Benjamin Franklin” on the side of some of their guns in the 1940s and ’50s.

With the poor English being taught in U.S. schools today, new shooters don’t realize that words in quotes don’t mean what they imply. It used to be a written way of smiling and winking; now it just confuses.

B.B. (Unrelated to the current topic). Is it alright to leave bulk-filled CO2 guns, e.g.,Tau, Drulov, and Alfa Proj charged when not in use? Perhaps over the blogs and reviews this has been covered but please give me your views. Thanks, —————Don

BB, I know what you’re saying about the Chinese B4-2, but I think it might be a bit better than that.

I’ve had a couple, and I’d suggest that these underlever rifles are definitely a couple of notches above the cheap B1 and B2 model breakbarrels that are frequently sold at similar prices. The design of the gun is much more solid, the machining and metal finish is superior, and the trigger design is infinitely better. All in all, these rifles are pretty robust. In comparison, the B1 and B2 breakbarrels are absolute garbage.

The B4-2 can be a very enjoyable and reliable plinker. No, it isn’t even as refined as a Crosman Quest – but at $30, the price of a medium-grade plastic airsoft pistol, it is a surprizingly usable rifle. Plus, at a little over 6 lbs, it gets the arms used to hefting something with some weight to it…

Yeah, I just found out that South Summit doesn’t list the B4-2 anymore. The B3 is similar – but I don’t know if it’s as good.

The poor quality B1 and B2 breakbarrels seem to come out of the Shanghai airgun factory, as do the B3, the B4-1 (TF41) and I believe the old TS45. So does the Beeman SS1000, TF97/QB36 and the TF99/QB36-2 that BB just tested. Supposedly the QB78 also is made at this factory.

The B4-2 seems to come from a different source, one that is shared with the B19/Crosman Quest, the B3/B7 sidelevers, B20/B26, the B21/B30 and the B40/B50.

QC from both can be spotty, but in my experience guns from the second group are generally made and finished better, and oinkers are less common.

Some maintain that the same factory makes all the above models, but I don’t think that’s true.